WO2023065128A1

WO2023065128A1 - Negative electrode sheet, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2023065128A1
Application number: PCT/CN2021/124798
Authority: WO
Inventors: 史东洋; 陈宁; 刘双双; 刘斯通
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2021-10-19
Filing date: 2021-10-19
Publication date: 2023-04-27
Also published as: KR20230058001A; JP2023550221A; CN116711099A; EP4199146A1; US20230117186A1; EP4199146A4

Abstract

The present application provides a negative electrode sheet, comprising a current collector and a coating coated on at least one surface of the current collector. The coating comprises a negative electrode active substance and metal powder. In the coating, the electrode potential of the metal powder with respect to lithium is 1.6-3.5 V, and the negative electrode active substance is a silicon-based material. With respect to the total mass of the silicon-based material and the metal powder, the proportion by mass of the metal powder is 5-20%, optionally 5-15%, and the proportion by mass of the silicon-based material is 80-95%, optionally 85-95%.

Description

Negative electrode sheet, secondary battery, battery module, battery pack and electrical device

technical field

The present application relates to the technical field of lithium-ion secondary batteries, in particular to a negative pole piece, a secondary battery, a battery module, a battery pack and an electrical device.

Background technique

In recent years, as the application range of lithium-ion secondary batteries has become more and more extensive, lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric Automotive, military equipment, aerospace and other fields. Due to the great development of lithium-ion secondary batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance. In addition, due to the increasingly limited choice of negative electrode active materials, silicon-based materials are considered to be the best choice to meet the requirements of high energy density.

However, when the silicon-based material is charged and discharged for the first time, a solid electrolyte interfacial film (SEI film) will be formed on the particle surface, and the SEI film will continue to decompose and generate heat, deteriorating the safety performance of the lithium-ion secondary battery. Therefore, the safety performance of existing lithium-ion secondary batteries using silicon-based materials still needs to be improved.

Contents of the invention

The technical problem to be solved by the invention

The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode sheet, the electrode potential of the metal powder contained in the negative electrode sheet is between 1.5 and 3.5V with respect to lithium, and therefore, without affecting the two. In the case of the capacity of the secondary battery, a large amount of metal can be precipitated before the negative electrode plate reaches the copper precipitation potential, causing a short circuit of the battery, thereby passing the over-discharge test of the secondary battery.

Technical solutions for problem solving

In order to achieve the above purpose, the present application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.

The first aspect of the present application provides a negative electrode sheet comprising: a current collector and a coating coated on at least one surface of the current collector, the coating includes a negative active material, metal powder, a conductive agent and an adhesive agent, wherein, in the coating, the electrode potential of the metal powder relative to lithium is between 1.6 and 3.5V, the negative electrode active material is a silicon-based material, and the electrode potential of the metal powder relative to the silicon-based material and the metal The total mass of the powder, the mass proportion of the metal powder is 5-20%, optionally 5-15%, the mass proportion of the silicon-based material is 80-95%, optionally 85%-95% .

Therefore, the present application adds metal powder with an electrode potential between 1.6 and 3.5V relative to lithium in the coating of the negative electrode sheet to improve the overdischarge process of the battery when the negative electrode potential reaches the oxidation potential of the metal powder. , the metal powder can be oxidized into metal ions before the copper foil current collector, and then pass through the separator, reduce and precipitate metal on the surface of the positive electrode sheet and pierce the separator, causing a short circuit in the lithium-ion secondary battery, so as not to affect the lithium-ion secondary battery. In the case of secondary battery capacity, pass the lithium-ion secondary battery over-discharge test. For the over-discharge test of the lithium-ion secondary battery, for example, the lithium-ion secondary battery is fully charged to 4.25V with a constant current of 0.33C rate, then charged to 0.05C with a constant voltage, left to stand for 1 hour, and discharged for 90V at a rate of 1C. minutes and observe at room temperature for 1 hour. If the battery does not catch fire or explode, it is considered that the lithium-ion secondary battery has passed the over-discharge test.

At the same time, the application uses the above-mentioned mass ratio of metal powder and silicon-based materials to ensure that a sufficient amount of metal is precipitated on the negative electrode sheet during the over-discharge test and pierces the diaphragm to cause an internal short circuit in the lithium-ion secondary battery, while minimizing the negative electrode. Too much metal powder in the sheet coating affects the gram capacity of the negative electrode, thereby reducing the adverse effect on the energy density of the lithium-ion secondary battery.

In any embodiment, the metal powder is one or more of Mn, Cr, Zn, Ga, Fe, Cd, Co, Ni, Tl, In, Sn, Pb, optionally, Mn, Co, One or more of Fe and Cr, further optionally, Dv50 of the metal powder=20nm-20μm, optionally, 50nm-10μm.

Therefore, the present application can pass the over-discharge test by selecting a metal element with a potential of 1.6-3.5 V to the lithium electrode, so that the lithium-ion secondary battery containing the negative electrode sheet of the present application can be passed. From the perspective of the safety performance and service life of the lithium-ion secondary battery, 1.6V is selected as the lower limit of the lithium electrode potential. The potential of the negative electrode of the lithium-ion secondary battery can reach around 1.5V under extreme conditions, so the potential value of the above-mentioned metal powder to the lithium electrode should be greater than 1.5V. At the same time, copper foil is usually used as the current collector for the negative pole piece, and the oxidation potential of the copper foil current collector is around 3.6V, so the potential of the metal powder to the lithium electrode should be lower than 3.5V in order to improve the over-discharge of the lithium-ion secondary battery The pass rate of the test. At the same time, from the perspective of the processing requirements of the negative electrode sheet, when the Dv50 of the metal powder is within the above range, the agglomeration of the slurry or scratches on the current collector during coating can be avoided.

In any embodiment, the silicon-based material is at least one of SiO _x , a mixture of SiO _x and graphite, wherein, relative to the total mass of the silicon-based material, the mass ratio of the SiO _x is 10- 30%, the mass proportion of the graphite is 70-90%, wherein, in the SiO _x , 0≤x<2. Optionally, the Dv50 of the SiO _x = 1-10 μm, and/or, the Dv50 of the graphite = 3-20 μm. Therefore, from the perspective of taking into account both the energy density and cycle performance of the lithium-ion secondary battery, the above-mentioned silicon-based material is selected as the negative electrode active material. When the Dv50 of the SiOx and the graphite is within the above range, the _SiOx and graphite are easily dispersed in the slurry, which is beneficial to the subsequent coating process.

In any embodiment, in the coating, compared with the total mass of the coating, the total mass ratio of the silicon-based material to the metal powder is 95-99%. Therefore, when the total mass ratio of the silicon-based material to the metal powder is within the above range, the negative electrode sheet not only supports sufficient silicon-based material as the negative electrode active material, but also contains an appropriate amount of metal powder. Therefore, The lithium-ion secondary battery comprising the negative pole piece not only has a higher energy density, but also can pass the over-discharge test.

A second aspect of the present application provides a secondary battery, including the negative electrode sheet of the first aspect of the present application.

A third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.

A fourth aspect of the present application provides a battery pack, including the battery module of the third aspect of the present application.

The fifth aspect of the present application provides an electric device, including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application. kind.

Invention effect

The present application provides a negative electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device. The coating of the negative electrode sheet of the present application contains silicon-based materials as the negative electrode active material and metal powder with a lithium electrode potential between 1.6 and 3.5V. The silicon-based material has a larger gram capacity, thereby improving the content of The energy density of the negative pole piece lithium ion secondary battery. By adding the metal powder, the passing rate of the over-discharge test of the lithium ion secondary battery is improved without affecting the capacity of the lithium ion secondary battery, thereby improving the safety performance of the lithium ion secondary battery.

Description of drawings

FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .

FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.

FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 5 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 4 .

FIG. 6 is a schematic diagram of an electrical device in which a secondary battery is used as a power source according to an embodiment of the present application.

Explanation of reference signs:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly

Detailed ways

Hereinafter, embodiments of the negative electrode sheet, secondary battery, battery module, battery pack, and electrical device of the present application will be specifically disclosed in detail with reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known items and repeated descriptions of substantially the same configurations may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

A "range" disclosed herein is defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instruction, all the steps of the present application can be performed sequentially, or randomly, or sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may also include steps (b) and (a) performed in sequence. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.

If there is no special description, the "comprising" and "comprising" mentioned in this application mean open or closed. For example, the "comprising" and "comprising" may mean that other components not listed may be included or included, or only listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by either of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist).

Negative pole piece

In one embodiment of the present application, the present application proposes a negative electrode sheet comprising a current collector and a coating coated on at least one surface of the current collector, the coating comprising a negative active material, metal powder, and a conductive agent. and an adhesive, wherein, in the coating, the electrode potential of the metal powder relative to lithium is between 1.6 and 3.5V, and the negative electrode active material is a silicon-based material, relative to the silicon-based material and The total mass of the metal powder, the mass proportion of the metal powder is 5-20%, optionally 5-15%, the mass proportion of the silicon-based material is 80-95%, optionally 85% ~95%.

Although the mechanism is not yet clear, the applicant has unexpectedly discovered through a large number of experiments that the application increases the electrode potential between 1.6 and 3.5V relative to lithium by adding metal powder in the coating of the negative electrode plate. During the over-discharge process of the battery, when the potential of the negative electrode reaches the oxidation potential of the metal powder, the metal powder can be oxidized into metal ions before the copper foil current collector, and then pass through the separator, reduce and precipitate metal on the surface of the positive electrode sheet and pierce the separator. The internal short circuit of the lithium-ion secondary battery is caused, so that the safety performance of the lithium-ion secondary battery is improved by passing the over-discharge test of the lithium-ion secondary battery without affecting the capacity of the lithium-ion secondary battery. For the over-discharge test of the lithium-ion secondary battery, for example, the lithium-ion secondary battery is fully charged to 4.25V with a constant current of 0.33C rate, then charged to 0.05C with a constant voltage, left to stand for 1 hour, and discharged for 90V at a rate of 1C. minutes and observe at room temperature for 1 hour. If the battery does not catch fire or explode, it is considered that the lithium-ion secondary battery has passed the over-discharge test.

In some embodiments, the metal powder is one or more of Mn, Cr, Zn, Ga, Fe, Cd, Co, Ni, Tl, In, Sn, Pb, optionally, Mn, Co, Fe, Cr, further optionally, Dv50 of the metal powder = 20nm-20μm, optionally, 50nm-10μm.

Therefore, the present application ensures that the lithium-ion secondary battery containing the negative electrode sheet of the present application can pass the over-discharge test by selecting metal elements with a lithium electrode potential between 1.6 and 3.5V. From the perspective of the safety performance and service life of the lithium-ion secondary battery, 1.6V is selected as the lower limit of the lithium electrode potential. The potential of the negative electrode of the lithium-ion secondary battery can reach around 1.5V under extreme conditions, so the potential value of the above-mentioned metal powder to the lithium electrode should be greater than 1.5V. At the same time, copper foil is usually used as the current collector for the negative pole piece, and the oxidation potential of the copper foil current collector is around 3.6V, so the potential of the metal powder to the lithium electrode should be lower than 3.5V in order to improve the over-discharge of the lithium-ion secondary battery The pass rate of the test. At the same time, from the perspective of the processing requirements of the negative electrode sheet, when the Dv50 of the metal powder is within the above range, the agglomeration of the slurry or scratches on the current collector during coating can be avoided.

In some embodiments, the silicon-based material is at least one of SiO _x , a mixture of SiO _x and graphite, wherein, relative to the total mass of the silicon-based material, the mass ratio of the SiO _x is 10- 30%, the mass proportion of the graphite is 70-90%, optionally, the Dv50 of the SiO _x = 1-10 μm, and/or, the Dv50 of the graphite = 3-20 μm. Wherein, 0≤x<2 in the SiO _x . Therefore, the present application selects the above-mentioned silicon-based material as the negative electrode active material from the perspective of ensuring the energy density and cycle performance of the lithium-ion secondary battery. When the Dv50 of the SiO _x and the graphite is within the above range, the silicon-based material and the graphite are easy to disperse in the slurry, which is beneficial to the subsequent coating process.

In some embodiments, in the coating, compared with the total mass of the coating, the total mass ratio of the silicon-based material to the metal powder is 95-99%. Therefore, when the total mass ratio of the silicon-based material to the metal powder is within the above range, the negative electrode sheet not only supports enough silicon-based material as the negative electrode active material, but also contains a sufficient amount of metal powder, Therefore, the lithium-ion secondary battery comprising the negative electrode sheet has a higher energy density and better performance in the over-discharge test.

In addition, the average volume distribution particle diameter Dv50 refers to the particle diameter corresponding when the cumulative volume distribution percentage of the negative electrode active material and the metal powder reaches 50%. In this application, the volume average particle diameter Dv50 of the negative electrode active material and the metal powder can be measured by laser diffraction particle size analysis. For example, with reference to the standard GB/T 19077-2016, use a laser particle size analyzer (such as Malvern Master Size 3000) to measure.

In addition, the secondary battery, the battery module, the battery pack, and the power consumption device of the present application will be described below with appropriate reference to the accompanying drawings.

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive pole piece, a negative pole piece, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode. The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, and the positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for batteries. As an example, the positive active material may include at least one of the following materials: olivine-structured lithium-containing phosphate, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials of batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also abbreviated as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also abbreviated as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also abbreviated as NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also may be abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon At least one of a composite material, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[Negative pole piece]

The negative pole piece is the negative pole piece according to the first aspect of the present application.

[Electrolyte]

The electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece. The present application has no specific limitation on the type of electrolyte, which can be selected according to requirements. For example, electrolytes can be liquid, gel or all solid.

In some embodiments, the electrolyte is an electrolytic solution. The electrolyte solution includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium difluorodifluorooxalatephosphate and lithium tetrafluorooxalatephosphate.

In some embodiments, the solvent may be selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of the battery, such as additives that improve battery overcharge performance, additives that improve high-temperature or low-temperature performance of batteries, and the like.

[Isolation film]

In some embodiments, a separator is further included in the secondary battery. The present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

In some embodiments, the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft case may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The present application has no special limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG. 1 shows a square-shaped secondary battery 5 as an example.

In some embodiments, referring to FIG. 2 , the outer package may include a housing 51 and a cover 53 . Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity. The positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the accommodating chamber. Electrolyte is infiltrated in the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 3 is a battery module 4 as an example. Referring to FIG. 3 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

4 and 5 show the battery pack 1 as an example. Referring to FIGS. 4 and 5 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric devices may include mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, etc.) , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited thereto.

As the electric device, a secondary battery, a battery module or a battery pack can be selected according to its use requirements.

FIG. 6 is an example of an electrical device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack or a battery module may be used.

As another example, a device may be a cell phone, tablet, laptop, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Example 1

Mix metal Mn powder with silicon-based materials, conductive carbon Super P, thickener sodium carboxymethylcellulose CMC, and binder SBR in deionized water according to the mass ratio of 96:1:1.2:1.8, and stir to obtain a uniform The negative electrode slurry is coated on one side of the slurry on the surface of the copper foil substrate, dried and rolled to prepare the negative electrode sheet.

Among them, the Dv50 of the metal Mn powder is 10 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Mn powder, the mass ratio of the silicon-based material to the metal Mn powder is 85:15.

Example 2

Among them, the Dv50 of the metal Mn powder is 20 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Mn powder, the mass ratio of the silicon-based material to the metal Mn powder is 90:10.

Example 3

Among them, the Dv50 of metal Mn powder is 5 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Mn powder, the mass ratio of the silicon-based material to the metal Mn powder is 90:10.

Example 4

Example 5

Mix metal Fe powder with silicon-based materials, conductive carbon Super P, thickener sodium carboxymethylcellulose CMC, and binder SBR in deionized water according to the mass ratio of 96:1:1.2:1.8, and stir to obtain a uniform The negative electrode slurry is coated on one side of the slurry on the surface of the copper foil substrate, dried and rolled to prepare the negative electrode sheet.

Among them, the Dv50 of the metal Fe powder is 10 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Fe powder, the mass ratio of the silicon-based material to the metal Fe powder is 90:10.

Example 6

Mix metal Co powder with silicon-based materials, conductive carbon Super P, thickener sodium carboxymethylcellulose CMC, and binder SBR in deionized water according to the mass ratio of 96:1:1.2:1.8, and stir to obtain a uniform The negative electrode slurry is coated on one side of the slurry on the surface of the copper foil substrate, dried and rolled to prepare the negative electrode sheet.

Among them, the Dv50 of metal Co powder is 5 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Co powder, the mass ratio of the silicon-based material to the metal Co powder is 95:5.

Example 7

Mix metal Cr powder with silicon-based materials, conductive carbon Super P, thickener sodium carboxymethylcellulose CMC, and binder SBR in deionized water according to the mass ratio of 96:1:1.2:1.8, and stir to obtain a uniform The negative electrode slurry is coated on one side of the slurry on the surface of the copper foil substrate, dried and rolled to prepare the negative electrode sheet.

Among them, the Dv50 of metal Cr powder is 5 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Cr powder, the mass ratio of the silicon-based material to the metal Cr powder is 95:5.

Comparative example 1

Dissolve the silicon-based material, conductive carbon Super P, thickener sodium carboxymethylcellulose CMC, and binder SBR in deionized water according to the mass ratio of 96:1:1.2:1.8, and obtain a uniform negative electrode slurry after stirring. Coating the slurry on the surface of the copper foil base material on one side, drying and rolling to prepare the negative electrode sheet.

Wherein, Dv50 of SiO=4 μm, Dv50 of graphite=13 μm, in the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%.

Comparative example 2

Among them, the Dv50 of the metal Mn powder is 10 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Mn powder, the mass ratio of the silicon-based material to the metal Mn powder is 98:2.

Comparative example 3

Among them, the Dv50 of the metal Mn powder is 20 μm, the Dv50 of SiO is 4 μm, and the Dv50 of graphite is 13 μm. In the silicon-based material, the mass proportion of graphite is 70%, and the mass proportion of SiO is 30%. Relative to the total mass of the silicon-based material and the metal Mn powder, the mass ratio of the silicon-based material to the metal Mn powder is 70:30.

The relevant parameters of the negative electrode sheets of the above-mentioned Examples 1-7 and Comparative Examples 1-3 are shown in Table 1 below.

Table 1: Relevant parameters of negative electrode sheets of Examples 1-7 and Comparative Examples 1-3

In addition, the negative electrode sheets obtained in the foregoing Examples 1-7 and Comparative Examples 1-3 were respectively prepared into secondary batteries as shown below, and performance tests were performed. The test results are shown in Table 2 below.

(1) Preparation of secondary battery

The positive electrode active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed in an N-methylpyrrolidone solvent system at a weight ratio of 94:3:3, and then coated on an aluminum foil and baked. Dry and cold press to obtain the positive electrode sheet.

The negative pole piece is selected from the negative pole piece in the above-mentioned embodiments and comparative examples.

A porous polymer film made of polyethylene (PE) is used as the separator. The positive pole piece, the separator and the negative pole piece are stacked in order, so that the separator is between the positive and negative poles to play the role of isolation, and the bare cell is obtained by winding. Put the bare cell in the outer package, inject the electrolyte and package it to obtain the secondary battery using the positive electrode sheet in each embodiment and comparative example.

(4) Secondary battery initial discharge capacity test

Each of the secondary batteries prepared above was placed in a constant temperature environment of 25°C for 39 minutes, discharged to 2.5V at 1/3C, charged to 4.25V at 1/3C after standing for 30 minutes, and then charged to 4.25V at 4.25V Charge at a constant voltage until the current is ≤0.05C, let it stand for 30 minutes, and then discharge to 2.5V according to 1/3C. The discharge capacity at this time is the initial discharge capacity, which is recorded as D0.

(2) Over-discharge test of secondary battery

According to the test method in GB38031-2020, the secondary battery in the above-mentioned embodiment and comparative example was selected to conduct an over-discharge test with a BT-2000 battery performance meter (manufacturer: Arbin, USA) and read the minimum reverse voltage: use 0.33 After C rate constant current full charge to 4.25V, then constant voltage charge to 0.05C, let it stand for 1 hour, discharge at 1C rate for 90 minutes, and observe at room temperature for 1 hour. If the battery does not catch fire or explode, it is considered to have passed the over-discharge test.

Table 2: Performance test results of Examples 1-7 and Comparative Examples 1-3

According to the above results, it can be seen that the negative electrode sheets in Examples 1 to 7 all contain an appropriate amount of silicon-based materials and metal powder, and the potential of the metal powder to the lithium electrode is between 1.6 and 3.5V. Therefore, in the over-discharge test, there is Good performance: the metal powder in the negative pole piece is oxidized into cations, then reduced and precipitated on the surface of the positive pole piece, and then pierces the separator, thereby forming a short circuit inside the secondary battery, thereby protecting the secondary battery from being damaged in the over-discharge test. Continuous heating and fire, improving the safety performance of the secondary battery.

In contrast, in Comparative Example 1, no metal powder with a potential of 1.6 to 3.5 V to the lithium electrode was added, and a small amount of the above-mentioned metal powder was added in Comparative Example 2. Therefore, the secondary batteries in Comparative Example 1 and Comparative Example 2 All failed to form a short circuit inside, the minimum reverse voltage was as high as 32.7V, and the internal heat of the battery continued to dissipate, which could not protect the secondary battery, thus passing the over-discharge test. Although the secondary battery in Comparative Example 3 can also pass the over-discharge test. However, if the content of metal powder in the negative pole piece is too high, the gram capacity of the secondary battery will be sacrificed and the energy density of the secondary battery will be affected.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same effects are included in the technical scope of the present application. In addition, without departing from the scope of the present application, various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

Claims

A negative pole piece, characterized in that,

comprising a current collector and a coating applied to at least one face of the current collector,

The coating includes negative electrode active material, metal powder,

Wherein, in the coating, the electrode potential of the metal powder relative to lithium is between 1.6 and 3.5V, and the negative electrode active material is a silicon-based material,

Relative to the total mass of the silicon-based material and the metal powder, the mass ratio of the metal powder is 5-20%, optionally, 5-15%,

The mass proportion of the silicon-based material is 80-95%, optionally, 85-95%.
The negative electrode sheet according to claim 1, characterized in that,

The metal powder is one or more of Mn, Cr, Zn, Ga, Fe, Cd, Co, Ni, Tl, In, Sn, Pb, optionally, one of Mn, Co, Fe, Cr species or several,

Further optionally, the Dv50 of the metal powder is 20 nm to 20 μm, optionally, 50 nm to 10 μm.
The negative electrode sheet according to claim 1 or 2, characterized in that,

The silicon-based material is at least one of SiO x , a mixture of SiO x and graphite, wherein, relative to the total mass of the silicon-based material, the mass ratio of the SiO x is 10-30%, and the graphite The mass proportion of is 70-90%, wherein, in the SiO x , 0≤x<2,

Optionally, the Dv50 of the SiO x = 1-10 μm, and/or, the Dv50 of the graphite = 3-20 μm.
The negative electrode sheet according to any one of claims 1 to 3, characterized in that,

In the coating, compared with the total mass of the coating, the total mass ratio of the silicon-based material to the metal powder is 95-99%.
A secondary battery, characterized by comprising the negative electrode sheet according to any one of claims 1-4.
A battery module comprising the secondary battery according to claim 5.
A battery pack, characterized by comprising the battery module according to claim 6.
An electrical device, characterized by comprising at least one selected from the secondary battery according to claim 5, the battery module according to claim 6, or the battery pack according to claim 7.